Electric vacuum furnace



3 Sheets-Sheet /l G D BAGLEY ELECTRIC VACUUM FURNACE Filed April 28, 1927 May 29, 1928.

INVENTOR: E 2 7! ATTORNEYS.

FIG. I.

Patented Ma y 29, 192 8.

UNITED "STATES PAT-ENT- or FICE. j

amp. BAGLEY, or GREAT NECK, NEW roux, ASSIGNOB T0. min xmm'r LABOBA-' I Teams 00. me, A coaroaunon or new roux. i

nmic'rmc vacuum summon.

. Q This invention relates to furnaces and more particularly to improvements in electrically heated vacuum furnaces of the type in which the heat chamber is sealed with mercury to.

permit sub-atmospheric pressure to be maintained therein.-

One of the objects of-my invention is to provide an electric furnace in which given temperaturesmay be obtained with less cur rent than has heretofore been required. Another object of my invention is to prevent the deposition of an opaque metallic film on the walls of the heating chamber especially when the latter is constructed of glass. An-

other object of my invention is to provide a yieldable' supporting contact for the heating elements to avoid buckling and tearing of this element. A still further object of my invention is to reduce the amount of mercury required to seal the furnace chamber.

These and other objects and the novel features of this inyention will be apparent from the following descriptionrtaken in connection with the accompanying drawings, in which:

Fig. 1 schematicallyillustrates a vertical section of an electric furnace embodying this Invention, certain parts being shown 1n ele- .vation;

' Fig. 2 is a detail sectional view of a portion of the furnace taken on the line 2-2 of Fig. 3; and

Fig. 3 is a' horizontal section taken on the line 3--3 of Fig. 2.

As illustrated,- the furnace comprises a steel tube 10 closed at its upper end. the upper interior of which provides a gas tight tionis carried on. It will be understood, however, that improvements herein disclosed are also applicable to furnaces of the type shown and described in other applications, in

cooled as by a draft. Moreover the glass may be of uneven thickness in which case the thinner portions may collapse when subject ed .to a high vacuum. By making the wall of metal itis possible to bring a cooling coil 20 into contact therewith, thus allowing the wall to be much closer to the resistor than is possiblewhen glass is used, with a consequent decrease in the space to be evacuated. A suitable cooling medium, such as water, is

Application filed April as, 1927. Serial N o. 187,249. i

circulated through this coil. The tube is provided with a suitable conduit 13 for the purpose of evacuating the chamber 11. At

the end of the tube suitable means 14 are provided for permitting an inspection of the interior of the furnace when a tube of opaque material is employed.

The tube 10is sealed by disposing the lower open end below the level of a body of' mercury 16 .in a reservoir '17. Inside the lower end, but spaced from and desirably concentric with it, is a tube 21 of suitable insulating material, such as glass or bakelite, which extends through a fluid tight joint in the bottom of the reservoir 17 and has its lower end sealed by a closure 18 and contains a second body of mercury 30. The reservoir 17 constitutes a seal for the chamber 11, is open to the atmosphere and is of a suitable size to hold the quantity of mercury required for the mercury column when the furnace is .highly evacuated. A cooling pipe 19 extends upwardly through the closure 18 and is closed at its upper end, The cooling fluid, ordinarily water, flows in through the pipe 19and out through a pipe 22 inside the pipe 19.

- The charge in the chamber 11 is electrically heated by means of a resistor 24 which is connected in series circuit with an electri cal conductor 25, the cooling elements 19, and the mercury 30. Ihe conductor 25 may be a rod or tubeof metal or any conducting material suited to-the current and temperature to be used. If the resistor is to be operated at a temperature above the melting chamber 11 in which the furnacing opera point of the conductor material, wateror other cooling medium may be circulated through the conductor. The legs of conductor 25, extend into opposite sides of the reservoir 17 through suitable mercury tight joints, thence up through the mercury 16 and the annular, space between the tubes 12 and 21 and into the chamber 10 where they are connectedby the bend 26. As shown, the conductors 25 and 19 and the respective columns of mercury through which theypass, are insulated from one another by the tube 21.- If desired the lower ends of the conductor 25 may be. bent under the lower edge of the tube. 10 and brought up through the mercury seal 16. Current .supply cables 28 and 29 may be secured to the conductors 25 and 19 respectively by suitable clamps, and rubber hose or other suitable means may be con led thereto for birculating cooling fluid tl erethrough.

The resistor 24 is adapted to surround the v furnace charge and is desirably in the form l of a cylinder formed by him ing together two elongated curved sheets 0 a refractory metal such as tungsten, molybdenum 'or the like. The parts of the vertical tubular re-' ,sistor are rigidly held at their upper ends and electrically connected to the conductor 25 by afcopper clamp 31 consisting of two similar sections clamped to the legs of the conductor by bolts 32. The bend 26 maybe curved soas not to obstruct the view through 14 into the upper end of the resistor.

.by the mercury thus relieving the resistor of its weight. The height of this column of mercury is preferably great enough to act as a seal against any leaks in the closure at the bottom of the insulating tube 21.

Since resistor 24 is rigidly attached at its upper end only, its lower end is free to move vertically to compensate for any expansion and contraction of resistor 24 and connected parts and thus eliminates the possibility of buckling or tearing the resistor through this cause. The contact 34' and the clamp 33 are cooled by the conduction of their heat-to the mercury within the tube 21, whence heat is carried away by the cooling medium within the tubes 19 and 22 which project into cavity 34 in the lower end of contact 34. A vent 41 for the cavity 34 provides for pressure equalization. The upper plamp 31- is kept cooled by the circulation of cooling fluid throu h the conductor and the tube 10 is coole by the circulation of a cooling medium through the coil 20. So cooledfthe' furnace can be operated at any temperature up to the melting point ofthe' resistor.

In order to conserve the energy required to operate the furnace I. have found it advantageous to provide a nonporous metallic radiation screen 35 'around'the resistor 24. This radiation screen may consist of a sheet iron cylinder concentric with. the resistor may emplo more than? one screen of the type descri ed, in which case it is evident t where 1i is "thenumberof concentric screens,

it beingassumed in this formula that the surface of e'ach screen is approximately equal to that of the resistor itself. TlllS of an opaque film on t e chamber wa l which at high temperature, especially when a mois especially objectionable when thechamber wall is of a trans arent material. I am radiation screen also revents the de osition occurs very rapidly in a high vacuum and I lybdenum' resistor is employed. This film l' aware that it has hitherto been .pro osed to i use means to prevent radiation consisting of an annular-graphite bo'x filled with graphite powder; but this structure contains a large amount of gas within its pores, which is given ofi at the low pressures employed within'th'e furnace, thereby makin it did!- cult to secure a high vacuum and I have :Fdund metallic radiation screens superior to such graphite screens.

, In order to reduce the amountof mercury required I may employ an annular displace" 'ment member 38 bet-ween tube 21 and the stem 12, the contacting and cooling member 23 being disposed'either within or without this annular member or still better-"in suitable vertical recesses in the side of the annular member 38, which may be of iron. This also reduces the surface of mercury subject to vaporization and lessens the amount of mercury'vapor which may find its wayinto the furnace chamber. I The operation of mydeviceis as follows: Toheat a charge to a high temperature under vacuum the seal at the tubular opening 13 is broken and the outer member 10.is

freely .lifted off exposing, the resistor 24. Thematerial to be heated is thenplaced inside the resistor in a suitable container and s and spaced therefrom a distance of about A the outer member '10.;is so replacedv as to 4f. While I may insulate thisscreenfrom the resistor by suitable discs of non contact lo i'isflformed of a transparent matieriah I.

55, ing material, I have found 'it sufficient to s ace it from the resistor and from one of 42 therein the purpose oft permitting the resistor observed and in order that the tntilpeiature of the'latter may be-measured wi' an 'optical pyrometerin case the tube submerge itsylower'end in themercury 16 thereby sealing" the chamber 11. The outlet 13 is then sealed to a vaeuum .pump and chamber 11 is evacuated. As the air is pumped One-mercury rises into the lower end of the tube? 10 approaching the barometric height, but sincethe tubes 10 and 21 are over 30 long the mercury doesnot rise intothe furnace chamber even with the highest 'vacua attainable. ,The: degree. of vacuum atmospheric is accurately determined by the use of gauges connected to the tube 13. Because of the relatively small volume of the chamber 11 as compared with furnaces employing a globe-shaped heating chamber, it is ossible to evacuate the chamber more quic 'ly and perform a greater number ofmeltings in a. given period.

When the. desired degree of vacuum has been reached circulation of the cooling medium is started and suitable electric. current is supplied by closing a switch in circuit with the cables .28 and 29. At the'end of a period of use the current is shut off and ressure is restored to the chamber 11 w en the charge and the resistor elements have cooled sufficiently to prevent oxidation or other deleterious action. At

that time the column of mercury within the tube will have dropped to its level in the reservoir 17 and the tube may be lifted ofi givin free access to the furnace charge.

I c aim:

1. An electric furnace comprising a gas tight chamber, a resistor therein, and a screen of substantially non-porous and dense material surrounding said resistor and reducin heat radiation from the latter.

- 2. n electric furnace according to claim 1 wherein said screen is, of metal.

3. An electric furnace according to claim 1 wherein said resistor and said screen are of tubular metal and concentric.

4. An electric furnace comprising a gas tight chamber, atubular metal resistor therein, and a tubular metal screen concentric with and surrounding said resistor, said screen being a non-current-carrying element and reducing heat radiation from said resistor. v

i 5. An electric furnace comprising a gas tight chamber, a resistor therein, a body of mercury sealing said chamber,.and a second body of mercury electrically connected to one end ofysaid resistor and arranged'to at least partially sup rt said. resistor so that the latter may fad expand and contract.

6. An electric furnace comprising a gas tight chamber, abody of mercury sealing said chamber, and second body of mercuryindependent of the first, and aresistor in said chamber having a contact 'at one end extending into and movable relative to said second body of. mercury. whereby said resistor and second body of mercury are electrically connected andsaid resistor is free to expand and'contract without distortion.

7. An electric furnace comprising a gas tight chamber, abody of mercury sealing;

said chamber, a hollow resistor in said chamber having a freely movable contact at one end; a conductor extending into said furnaceand a-seco'nd body of mercury providing an electrical connection between resistor.

contact and said conductor.

. insulating tube sai closed at its upper end' to 8. An electric furnace according to claim 7 wherein said conductor comprises means for circulating cooling medium relatively to curv cooperating with said wall to seal said chamber, an insulating tube within said wall,

a resistor in. said chamber having a contactdepending into said tube, a conductor extending intosaid tube, and a body of mercury in said tube electrically connecting said conductor to saidcontact and at least partially supporting the latter and said resistor.

10. An electric furnace comprising a chamber having a tubular wall, a body of mercury cooperating with said wall to provide a barometric seal for said chamber, an within and spaced from said wall, a conductor extending into said tube, a resistor in said chamber havin a contact in said tube in circuit with, but reely movable relatively to said conductor, and a solid annular member in the space between such tube and wall to reduce the volume oimercur required to form a barometric seal for chamber. 7

g 11. An electric furnace comprising a vertical metal tube open at its lower end and provide a furnace chamber within said upper end, a body of mercury cooperating wit said lower end to provide a barometric seal for said chamber, an insulating tube rojecting into said metal tube through the ower end thereof, a resistor in said chamber "having a contact depending into said insulatingtube, a conductor in said insulating tube and a body of mercury in said insulating tube electrically connecting said contact to said conductor.

12. An electric furnace comprising a chamber having a cylindrical bottom portion, a heating element within said chamber, electrically insulated concentric columns of mercury within said bottom outer column forming a barometric seal for said chamber and the inner column serving as means for partially supporting and conducting current to one of the terminals of said heating element.

13. An electric furnace compri ing; a

i portion, the

tubular ,wall of substantially uniform diameter providing a furnace chamber therein adjacent oneend, means cooperating with the other end of said wall to seal said chamber, a resistor in said chamberyand means for cooling said wall. y ,l l. An electric furnace according-to claim 13 wherein such wall is of'metal. andlsuch cooling means rcomprises a cooling coil in contact with said wall.

In testimony whereof, I ailix signature.

GLEN D. BAQLEY. r 

